fix(apt): cache snapshot collision checks

Cache the complete snapshot-name listing once per hook invocation instead\nof querying ZFS separately for every dataset and counter candidate. This\nremoves the repeated full-pool scan that becomes expensive when recursive\nsnapshot histories are large.\n\nCache the operation suffix as well and return an explicit success status\nfrom snapshot-name generation so collision retries are unambiguous. Ignore\nAPT configuration-only records because they do not represent package data\nchanges requiring a new pre-install snapshot.

apt-zfs-snapshot.sh

@@ -7,6 +7,8 @@ declare -r zfs_property='space.quico:auto-snapshot'
 declare -r zfs_property_value='true'
 declare -r zfs_max_name_length=255
 
+set -xv
+
 if [[ -r "${config_file}" ]]; then
     # shellcheck disable=SC1090
     source "${config_file}"
@@ -33,6 +35,7 @@ mixed_suffix="${mixed_suffix:-mixd}"
 package_separator="${package_separator:-:}"
 
 declare -a packages operations
+declare existing_snapshots
 
 print_msg() {
     local level="$1" message="$2"
@@ -77,7 +80,9 @@ parse_apt_input() {
 
         read -r package old_version _old_arch direction new_version _new_arch _multiarch action <<<"${line}"
         [[ -n "${package}" ]] || continue
-        if [[ "${action}" == '**REMOVE**' ]]; then
+        if [[ "${action}" == '**CONFIGURE**' ]]; then
+            continue
+        elif [[ "${action}" == '**REMOVE**' ]]; then
             add_package "${package}" 'remove'
         elif [[ "${direction}" == '>' ]]; then
             add_package "${package}" 'downgrade'
@@ -157,17 +162,18 @@ shorten_packages() {
     package_list="${value}"
 }
 
-existing_snapshot() { zfs list -H -t snapshot -o name | grep -Fxq -- "$1"; }
+existing_snapshot() { grep -Fxq -- "$1" <<<"${existing_snapshots}"; }
 
 make_snapshot_name() {
     local counter="$1" dataset base
     names=()
     for dataset in "${snappable_datasets[@]}"; do
-        base="${dataset}@${snapshot_prefix}${field_separator}${date_string}${field_separator}${counter}${field_separator}op:$(operation_suffix)${field_separator}sev:${severity}${field_separator}pkgs:${package_list}"
+        base="${dataset}@${snapshot_prefix}${field_separator}${date_string}${field_separator}${counter}${field_separator}op:${operation_suffix_result}${field_separator}sev:${severity}${field_separator}pkgs:${package_list}"
         (( ${#base} <= zfs_max_name_length )) || { print_msg ERR "Snapshot name exceeds ${zfs_max_name_length} characters: ${base}"; return 2; }
         names+=("${base}")
         existing_snapshot "${base}" && return 1
     done
+    return 0
 }
 
 prune_snapshots() {
@@ -196,9 +202,11 @@ main() {
     (( ${#packages[@]} > 0 )) || { print_msg INFO 'No package actions received; skipping snapshot'; return 0; }
     get_datasets
     (( ${#snappable_datasets[@]} > 0 )) || { print_msg INFO "No eligible ZFS datasets; skipping snapshot"; return 0; }
+    existing_snapshots="$(zfs list -H -t snapshot -o name)"
     date_string="$(TZ="${timezone}" date +"${date_format}")"
     severity_and_packages
     shorten_packages
+    operation_suffix_result="$(operation_suffix)"
     while :; do
         make_snapshot_name "$((++counter))"
         case "$?" in